This invention relates to a method for the measurement of the movement of colloidal particles in suspension or in solution, particularly for the treatment of water in order to determine the optimum dose of coagulant necessary for clarification or for regulating the addition of coagulant.
At the present time, such measurements are carried out using equipment possessing a certain number of disadvantages.
Within the framework of the treatment of water or effluent for example, a very simple method is applied, which consists of carrying out a coagulation test by reproducing te operating conditions of a clarifier. This method makes use of a primitive plant and requires large quantities of water, and in addition, it takes a long time and is not very accurate.
Another and more developed method consists of measuring the charge of the colloidal particles by the addition of an excess of polyelectrolytes and return colorimetric titration of this excess, this titration possessing the disadvantage of being very difficult to carry out.
In addition, installations exist which measure the movement of the colloidal particles in an electrical field.
It is well-known that the stability of colloidal suspensions or solutions is intimately associated with the value, in the receiving medium, of the electrokinetic potential of the particles encountered.
The value of this electrokinetic potential is expressed notably by the movement of the particles in an electrical field. Under these conditions, the measurement of this movement is a means of determining the electrokinetic potential, and therefore of studying the destabilisation by coagulation of colloidal solutions. This movement is well-known under the name of electrophoresis.
The known apparatus for the measuring of electrophoresis is composed of three parts, i.e. two compartments each containing an electrode, connected to each other by a tube which may have a length of approximately 10 cm and a diameter of approximately 4.5 mm. An electrical field of the order of 30 V/cm is created by the application of voltages ranging from 200 to 300 V direct current.
By means of local illumination using an incandescent lamp, the movement of the colloids in the tube is measured optically, using binoculars, one of the oculars of which comprise a micrometer, or again illumination is carried out using a laser, the movement of the colloids being then followed automatically.
All these known installations possess certain inherent disadvantages:
They necessitate the use of statistical measurements. In effect, the distribution of the colloids observed in a liquid is not homogeneous. Certain particles move rapidly, and others move slowly and thus do not react in the same way to a coagulating action. Therefore the individual mobility of each particle is measured.
They are difficult to handle.
They are expensive.